Integrated Photonic Electromagnetic Field Sensor Based on Broadband Bowtie Antenna Coupled Silicon Organic Hybrid Modulator

We present the design, fabrication and characterization of a compact and highly sensitive integrated photonic electromagnetic field sensor based on a silicon-organic hybrid modulator driven by a bowtie antenna. Slow-light effects in the electro-optic (EO) polymer refilled silicon slot photonic crystal waveguide (PCW), together with broadband electric field enhancement provided by the bowtie antenna, are utilized to enhance the interaction of microwaves and optical waves, enabling an ultra large effective in-device EO coefficient over 1000 pm/V and thus a high sensitivity. The EO polymer refilled slot PCW is designed for low-dispersion slow-light propagation, high poling efficiency, and high optical mode confinement inside the slot. The bowtie antenna acts not only as a receiving antenna, but also as poling electrodes during the fabrication process. A bowtie antenna integrated on doped silicon slot PCW is demonstrated to have a broad operational bandwidth, with a maximum resonance at the frequency of 10 GHz. The strongly enhanced broadband electric field is used to directly modulate the phase of the optical waves propagating through the slot PCW embedded inside the feed gap of the bowtie antenna. The phase modulation is then converted to intensity modulation using an external reference arm to form a Mach-Zehnder interferometer in our experimental setup. The sensing of electromagnetic field at 8.4 GHz is experimentally demonstrated, with a minimum detectable electromagnetic power density of $8.4\, {\rm mW\!/\!m}^{2}$ , corresponding to a minimum detectable electric field of 2.5 V/m.